Process for direct urea injection with selective catalytic reduction (SCR) for NOx reduction in hot gas streams and related systems and assemblies

ABSTRACT

A boiler or other fired vessel includes a housing with a burner at one end, a furnace downstream of the burner, a convection section downstream of the furnace and a flue gas outlet downstream of the convection section. A first means for loading a reducing agent comprising at least two injectors is located downstream of the furnace. A second means for loading a reducing agent is located downstream of the first means for loading a reducing agent. A selective catalytic reduction catalyst is located either downstream of the second means for loading a reducing agent or adjacent the second means for loading a reducing agent such that the catalyst is provided to the boiler or other fired vessel approximately simultaneously with the reducing agent from the second means for loading the reducing agent.

FIELD OF THE INVENTION

The present invention relates, generally, to the field of NO_(x)reduction. More particularly, the present invention relates to SCR forNO_(x) reduction in boilers and other fired vessels.

BACKGROUND OF THE INVENTION

The ever-increasing emissions from combustion sources have led toincreasing efforts to reduce fugitive emissions from these sources.Existing measures for NO_(x) (nitrogen oxides) reduction in boilersinclude two-stage combustion, exhaust gas recirculation, rapid mixburners, high excess air with air/fuel pre-mixed and the like. Intwo-stage combustion, combustion air is supplied in two stages to theburner, where the fuel is burned with a smaller amount of air thannecessary for complete combustion in the first stage, and the remainingamount of air necessary for complete combustion is supplied in thesecond stage, thereby lowering peak combustion temperatures and reducingNO_(x) formation. In exhaust gas recirculation, exhaust gas generated bycombustion is re-circulated so as to be mixed with the combustion airand fed to the burner, thereby also lowering peak combustiontemperatures and reducing NO_(x) formation. Rapid mix burners employboth exhaust gas recirculation (e.g., flue gas recirculation) and arapid mix of fuel and air in the burner. The rapid mix promotes air/fueldistribution in the flame which reduces localized high temperatures inthe flame which reduces NO_(x) formation. Pre-mix burners mix fuel andair just prior to combustion to provide uniform air/fuel mixturescombined with high excess air to reduce NO_(x) formation.

While these known methods have been effective at reducing NO_(x)formation, the reduction has come at the cost of at least some reductionin boiler performance. For example, in at least some respects, boilersemploying the above methods show a diminished response to load changes,an increase in the horsepower necessary for the combustion air fan motorto move the additional volumes of air, and an increase in operatingcosts due to an increased electrical energy demand.

Selective catalytic reduction (SCR), using post-combustion oxidationcatalysts to reduce NO_(x), has been an effective means for reducingNO_(x) emissions without sacrificing boiler performance. In SCR, anammonia source is required for the oxidation catalyst to remove NO_(x)from the boiler flue gases. Anhydrous ammonia is the most readily usablesource of ammonia in SCR applications. However, anhydrous ammonia posessignificant safety hazards if the boiler system leaks or fails.Anhydrous ammonia has a health hazard rating of 3 on a scale of 0 to 4,with even short exposure capable of causing serious temporary orresidual injury, even if prompt medical care is given. Eye washstations, ambient ammonia sensors, and alarms are required to manage thehealth hazards of anhydrous ammonia. Moreover, many boiler installationsare in hospitals, schools, prisons and universities where a large, andsometimes already susceptible or weak, population could be exposed toanhydrous ammonia during a leak or failure. This could be catastrophic.

Some boilers now employ aqueous methods of ammonia or reducing urea toammonia to avoid some of the health risks associated with storing largeamounts of anhydrous ammonia. Urea is particularly attractive to use inNo_(x) reduction systems as urea has a health hazard rating of 1 on ascale of 0 to 4, with short exposure potentially causing irritation butonly minor residual injury even if no treatment is given. Boilers whichincorporate methods of reducing urea to ammonia typically employadditional external heat sources and methods to convert urea to ammoniaexternal to the boiler or through various ducts and side streams of fluegas before adding dilution air to the ammonia for delivery through anammonia injection grid located upstream from the catalyst bed.

Delivering the oxidizing agent in these systems to the flue gas requiresexternal ducting with heat tracing, insulation, hot gas fans, and othercomponents. Failure of the heat tracing or insulation systems results infouling of the delivery system causing unscheduled shut-down andmaintenance. Moreover, these systems and added components increase thecomplexity and cost of boiler systems, increase the average maintenancecosts of the boiler, and consume a larger amount of energy to deliverthe oxidizing agent to the flue gas stream.

For at least these reasons, therefore, it would be advantageous if a newor improved method for SCR NO_(x) reduction could be developed thataddressed one or more of the above-described concerns, and/or otherconcerns. Particularly, it would be advantageous if a new or improvedmethod for SCR NO_(x) reduction could be provided for the low emissiondemands of the regulatory environment and the efficiency and performancedemands for reduced energy costs, and without sacrificing safety.

SUMMARY OF THE INVENTION

In accordance with one embodiment, disclosed herein is a boiler or otherfired vessel assembly.

In accordance with one embodiment, disclosed herein is a boiler or otherfired vessel assembly comprising a housing comprising a burner at afirst end, a furnace downstream of the burner, a convection sectiondownstream of the furnace, and a flue gas outlet downstream of theconvection section; a first means for loading a reducing agent into thehousing, wherein the first means for loading the reducing agent islocated downstream of the furnace and comprises at least two injectors;a second means for loading a reducing agent into the housing, whereinthe second means for loading the reducing agent is located downstream ofthe first means for loading the reducing agent and comprises at leastone injector; and a selective catalytic reduction (SCR) catalyst locatedeither downstream of the second means for loading a reducing agent intothe housing or adjacent the second means for loading a reducing agentinto the housing such that the SCR catalyst is provided to the boilerapproximately simultaneously with the reducing agent from the secondmeans for loading the reducing agent into the housing.

In accordance with a further embodiment, disclosed herein is a boiler orother fired vessel assembly comprising a housing comprising a burner, anintermediate furnace, a convection section downstream from theintermediate furnace, and a flue gas outlet downstream of the convectionsection; a first means for loading a reducing agent into the housing,wherein the first means for loading the reducing agent is locateddownstream of the furnace and comprises at least two injectors; a secondmeans for loading a reducing agent into the housing, wherein the secondmeans for loading the reducing agent is located downstream of the firstmeans for loading the reducing agent and comprises at least oneinjector; and a selective catalytic reduction (SCR) catalyst locatedeither downstream of the second means for loading a reducing agent intothe housing or adjacent the second means for loading a reducing agentinto the housing such that the SCR catalyst is provided to the boilerapproximately simultaneously with the reducing agent from the secondmeans for loading the reducing agent into the housing.

In accordance with a further embodiment, disclosed herein is a method ofreducing NO_(x) in a boiler or other fired vessel which produces adirect flame.

In accordance with a further embodiment, disclosed herein is a method ofreducing NO_(x) in a boiler or other fired vessel which produces adirect flame, the method comprising providing (a) a first amount of areducing agent to the boiler or other fired vessel at a first locationdownstream of the direct flame when a temperature of the first locationis greater than or equal to a threshold temperature, or (b) a secondamount of reducing agent to the boiler or other fired vessel at a secondlocation downstream of the direct flame when a temperature of the firstlocation is less than the threshold temperature, wherein the firstlocation is downstream of the second location; and providing a selectivecatalytic reduction catalyst either downstream of or at generally thesame location as second amount of a reducing agent, wherein the secondamount of reducing agent is provided using at least two injectors.

In accordance with a further embodiment, disclosed herein is a method ofretrofitting a boiler or other fired vessel the boiler or other firedvessel comprising a housing with a burner, an intermediate furnace, aconvection section downstream of the furnace, and a flue gas outletdownstream of the convection section, with a NO_(x) removal system.

In accordance with a further embodiment, disclosed herein is a method ofretrofitting a boiler or other fired vessel, the boiler or other firedvessel comprising a housing with a burner, an intermediate furnace, aconvection section downstream of the furnace, and a flue gas outletdownstream of the convection section, with a NO_(x) removal system, themethod comprising determining one or more parameters of the boiler orother fired vessel, wherein at least one of the one or more parametersis selected from the group consisting of internal shape of the boiler orother fired vessel, internal shape of the furnace, internal shape of theconvection section, internal shape of the flue gas outlet, peaktemperature of the furnace, peak temperature of the convection section,peak temperature of the flue gas outlet, operable temperature range ofthe furnace, operable temperature range of the convection section,operable temperature range of the flue gas outlet, concentration rangeof NO_(x) formation, operable firing range, type of NO_(x) compounds andconcentration range of one or more types of NO_(x) compounds, operatingconditions causing peak NO_(x) formation and combinations thereof;determining one or more parameters of a NO_(x) removal system, whereinat least one of the one or more parameters is selected from the groupconsisting of SCR catalyst to be used, reducing agent to be used, numberof reducing agent loading points, locations of reducing agent loadingpoints, type of means for loading reducing agent, timing of reducingagent loading at each reducing agent loading point, concentration ofreducing agent loading at each reducing agent loading point, spraypattern of the means for loading reducing agent at each reducing agentloading point, dilution or dilution range of the reducing agent, andcombinations thereof; providing, based on the one or more parameters ofthe NO_(x) removal system, a first means in communication with thehousing for providing a reducing agent into the housing of the boiler orother fired vessel downstream of the furnace, wherein the first meanscomprises at least two injectors; providing, based on the one or moreparameters of the NO_(x) removal system, a second means in communicationwith the housing for providing a reducing agent into the housing of theboiler or other fired vessel downstream of the first means for providingreducing agent; and providing, based on the one or more parameters ofthe NO_(x) removal system, a selective catalytic reduction catalystdownstream from or simultaneously with the second means for providing areducing agent.

In accordance with a further embodiment, disclosed herein is a boilerassembly.

In accordance with a further embodiment, disclosed herein is a boilerassembly comprising a housing comprising a burner at a first end, afurnace downstream of the burner, a convection section downstream of thefurnace, and a flue gas outlet downstream of the convection section; afirst means for loading a reducing agent into the housing, wherein thefirst means for loading the reducing agent is located downstream of thefurnace and comprises at least two injectors; a second means for loadinga reducing agent into the housing, wherein the second means for loadingthe reducing agent is located downstream of the first means for loadingthe reducing agent and comprises at least one injector; and a selectivecatalytic reduction (SCR) catalyst located either downstream of thesecond means for loading a reducing agent into the housing or adjacentthe second means for loading a reducing agent into the housing such thatthe SCR catalyst is provided to the boiler approximately simultaneouslywith the reducing agent from the second means for loading the reducingagent into the housing.

In accordance with a further embodiment, disclose herein is a boilerassembly comprising a housing comprising a burner, an intermediatefurnace, a convection section downstream from the intermediate furnace,and a flue gas outlet downstream of the convection section; a firstmeans for loading a reducing agent into the housing, wherein the firstmeans for loading the reducing agent is located downstream of thefurnace and comprises at least two injectors; a second means for loadinga reducing agent into the housing, wherein the second means for loadingthe reducing agent is located downstream of the first means for loadingthe reducing agent and comprises at least one injector; and a selectivecatalytic reduction (SCR) catalyst located either downstream of thesecond means for loading a reducing agent into the housing or adjacentthe second means for loading a reducing agent into the housing such thatthe SCR catalyst is provided to the boiler approximately simultaneouslywith the reducing agent from the second means for loading the reducingagent into the housing.

In accordance with a further embodiment, disclosed herein is a method ofreducing NO_(x) in a boiler which produces a direct flame.

In accordance with a further embodiment, disclosed herein is a method ofreducing NO_(x) in a boiler which produces a direct flame, the methodcomprising providing (a) a first amount of a reducing agent to theboiler at a first location downstream of the direct flame when atemperature of the first location is greater than or equal to athreshold temperature, or (b) a second amount of reducing agent to theboiler at a second location downstream of the direct flame when atemperature of the first location is less than the thresholdtemperature, wherein the first location is downstream of the secondlocation; and providing a selective catalytic reduction catalyst eitherdownstream of or at generally the same location as second amount of areducing agent, wherein the first amount of reducing agent is providedusing at least two injectors.

In accordance with a further embodiment, disclosed herein is a method ofretrofitting a boiler, the boiler comprising a housing with a burner, anintermediate furnace, a convection section downstream of the furnace,and a flue gas outlet downstream of the convection section, with aNO_(x) removal system.

In accordance with a further embodiment, disclosed herein is a method ofretrofitting a boiler, the boiler comprising a housing with a burner, anintermediate furnace, a convection section downstream of the furnace,and a flue gas outlet downstream of the convection section, with aNO_(x) removal system, the method comprising determining one or moreparameters of the boiler, wherein at least one of the one or moreparameters is selected from the group consisting of internal shape ofthe boiler or other fired vessel, internal shape of the furnace,internal shape of the convection section, internal shape of the flue gasoutlet, peak temperature of the furnace, peak temperature of theconvection section, peak temperature of the flue gas outlet, operabletemperature range of the furnace, operable temperature range of theconvection section, operable temperature range of the flue gas outlet,concentration range of NO_(x) formation, operable firing range, type ofNO_(x) compounds and concentration range of one or more types of NO_(x)compounds, operating conditions causing peak NO_(x) formation andcombinations thereof; determining one or more parameters of a NO_(x)removal system, wherein at least one of the one or more parameters isselected from the group consisting of SCR catalyst to be used, reducingagent to be used, number of reducing agent loading points, locations ofreducing agent loading points, type of means for loading reducing agent,timing of reducing agent loading at each reducing agent loading point,concentration of reducing agent loading at each reducing agent loadingpoint, spray pattern of the means for loading reducing agent at eachreducing agent loading point, dilution or dilution range of the reducingagent, and combinations thereof; providing, based on the one or moreparameters of the NO_(x) removal system, a first means in communicationwith the housing for providing a reducing agent into the housing of theboiler downstream of the furnace, wherein the first means comprises atleast two injectors; providing, based on the one or more parameters ofthe NO_(x) removal system, a second means in communication with thehousing for providing a reducing agent into the housing of the boilerdownstream of the first means for providing reducing agent; andproviding, based on the one or more parameters of the NO_(x) removalsystem, a selective catalytic reduction catalyst downstream from orsimultaneously with the second means for providing a reducing agent.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of the present disclosure which are believed to be novel areset forth with particularity in the appended claims. Embodiments of thedisclosure are disclosed with reference to the accompanying drawings andare for illustrative purposes only. The disclosure is not limited in itsapplication to the details of construction or the arrangement of thecomponents illustrated in the drawings. The disclosure encompasses otherembodiments and is capable of being practiced or carried out in othervarious ways. The drawings illustrate a best mode presently contemplatedfor carrying out the invention Like reference numerals are used toindicate like components. In the drawings:

FIG. 1A is a schematic cross-sectional view of a NO_(x) reduction systemin use in a firetube boiler showing direct injection at the furnace inaccordance with embodiments of the present disclosure;

FIG. 1B is a schematic rear view of the NO_(x) reduction system in usein a firetube boiler of FIG. 1A in accordance with embodiments of thepresent disclosure;

FIG. 2A is a schematic cross-sectional view of an alternative NO_(x)reduction system in use in a firetube boiler showing direct injection atthe flue gas outlet in accordance with embodiments of the presentdisclosure;

FIG. 2B is a schematic rear view of the alternative NO_(x) reductionsystem in use in a firetube boiler of FIG. 2A in accordance withembodiments of the present disclosure;

FIG. 3A is a schematic cross-sectional view of an alternative NO_(x)reduction system in use in a firetube boiler showing direct injection atboth the furnace and flue gas outlet in accordance with embodiments ofthe present disclosure; and

FIG. 3B is a schematic rear view of the alternative NO_(x) reductionsystem used in a firetube boiler of FIG. 3A in accordance withembodiments of the present disclosure.

FIG. 4 is a schematic cross-sectional view of a NO_(x) reduction systemin use in a watertube boiler showing direct injection at the furnace inaccordance with embodiments of the present.

FIG. 5 is a schematic cross-sectional view of a further alternativeNO_(x) reduction system used a watertube boiler showing direct injectionat the flue gas outlet in accordance with embodiments of the presentdisclosure; and

FIG. 6 is a schematic cross-sectional view of a further alternativeNO_(x) reduction system used in a watertube boiler showing directinjection at both the furnace and the flue gas outlet in accordance withembodiments of the present disclosure.

DETAILED DESCRIPTION

In accordance with one embodiment, a NO_(x) reduction system for use ina boiler or other fired vessel is disclosed. In an embodiment, a boileror other fired vessel includes, but is not limited to, a gas and/or oilfired burner, a steam boiler with or without superheat, a hot waterboiler or a thermal fluid heater of the firetube or watertube type.

FIGS. 1A-3 and 4-6 illustrate exemplary boiler configurations 101/101 awherein fuel and air are combusted by a burner 102 positioned near thefront end of a furnace 118 to form a flame 103 and hot combustion gases(or exhaust gases) 104. The hot combustion gases 104 pass from thecombustion chamber (where combustion occurs and the flame is located),to the convection section of the boiler where a fluid medium (e.g.,water) is heated. The hot exhaust gases 104 continue through theconvection section and are released through the flue gas outlet 110.

The boiler configurations 101/101 a of FIGS. 1A-3B and 4-6,respectively, differ in that FIGS. 1A-3B illustrate a firetube boiler101 while FIGS. 4-6 illustrate a watertube boiler 101 a. As shown inFIGS. 1A-3B, the hot combustion gases 104 transition from the combustionchamber to the convection section via a rear turn around area 105. Thehot combustion gases 104 are then directed through a plurality ofconvection tubes 106. Heat is transferred from the exhaust gases 104 tothe surrounding medium 107 (typically a liquid such as water). Steamcollects in the steam dome 108 and can be vented through a steam outlet(not shown). The cooling exhaust gases 104 are vented through the fluegas outlet 110. In an embodiment, the flue gas outlet 110 may be made ofround outlet ducts or rectangular outlet ducts. In contrast, as shown inFIGS. 4-6, in a watertube boiler 101 a, the hot combustion gases 104travel to the end of the furnace 118 and enter the hot end of theconvection zone 115. The hot, though starting to cool, combustion gases104 continue to travel through the convection zone through which anumber of convection tubes 106 pass, each convection tube 106 containinga medium to be heated (typically a liquid such as water). Heat from theexhaust gases 104 warms the liquid in the tubes 106, and any generatedsteam is released via a steam outlet (not shown). The cooling exhaustgases 104 are vented through the flue gas outlet 110.

In the embodiments shown, each boiler configuration 101/101 a furtherincludes a NO_(x) removal system 100/100 a/100 b. In the embodimentsshown, a NO_(x) removal system 100/100 a/100 b includes a reducing agent130, a means for loading the reducing agent 150 to the boilerconfiguration 101/101 a at least one location located downstream of theflame 103, and a NO_(x) removal catalyst (or SCR catalyst) 111.

In one embodiment, such as shown in FIGS. 1A, 2A, 4 and 5, a singlemeans for loading the reducing agent 150 is provided at a singlelocation downstream of the flame 103. Particularly, in FIGS. 1A and 4,the single means for loading the reducing agent 150 is positionedupstream of the convection section of the boiler configuration 101/101a, and in FIGS. 2A and 5, the single means for loading the reducingagent 150 is positioned at the flue gas outlet 110. More particularly,as shown in FIG. 1A, a single means for loading the reducing agent 150is provided at the rear turn around space 105, while the single meansfor loading the reducing agent 150 for the embodiment shown in FIG. 4 ispositioned at the point at which the hot combustion gases 104 enter thehot end of the convection area. Loading the reducing agent 130 at thepoint at which the hot combustion gases 104 enter the convection sectioncauses the reducing agent to be loaded in cross-flow with the combustiongas stream, i.e., hot combustion gases 104.

In other embodiments, however, multiple means for loading the reducingagent 150 may be provided either at or about the same general locationor, as show specifically in FIGS. 3A, 3B and 6, at different locationson a boiler configuration 101/101 a, provided each of the means forloading the reducing agent 150 is downstream of the flame 103. In apreferred embodiment, a NO_(x) removal system includes at least twomeans for loading the reducing agent 150, each provided at a differentlocation on a boiler configuration 101/101 a, and more preferably, aNO_(x) removal system includes at least two means for loading thereducing agent 150, wherein a first of the at least two means forloading the reducing agent 150 is positioned at the convection sectionand a second of the at least two means for loading the reducing agent150 is positioned at the flue gas outlet 110, as shown with respect toNO_(x) removal systems 100 b in FIGS. 3A, 3B and 6.

In an embodiment, a means for loading the reducing agent 150 can be anystructure(s), device(s) or combination of structure(s) and/or device(s)capable of loading a reducing agent into the boiler configuration101/101 a at the location intended. For example, in the particularembodiments shown in FIGS. 1A-6, each means for loading the reducingagent 150 comprises one or more injectors. However, in furtherembodiments, the means for loading the reducing agent 150 may comprise,without limitation, one or more openings or inlets (e.g., to permitpassage of a reducing agent), one or more nozzles, one or moreinjectors, one or more sprayers and/or any combination thereof.

In accordance with embodiments of the present disclosure, each means forloading the reducing agent 150 comprises one or more injectors, and moreparticularly, one or more lances with a hollow cone spray pattern. In afurther embodiment, one or more of the means for loading the reducingagent 150 used in a NO_(x) removal system 100/100 a/100 b comprises twoor more injectors. More particularly, the means for loading the reducingagent 150 as shown in FIGS. 1A-6 each comprise one or more, preferablytwo or more, atomizing lances, each comprising one or more, preferablytwo or more, nozzle heads or jet nozzle head for releasing the reducingagent.

In embodiments in which the means for loading the reducing agent 150includes one or more injectors, it will be understand that many types ofinjectors may be used. For example, injectors may be manually activatedor automated, have different types of heads (e.g., nozzle, jet, etc.),have one or more nozzle or jet heads, have different spray patterns(e.g., narrow cone. wide cone, hollow cone, bent stream, split stream,etc.), and/or injectors that use pressure, air or water (e.g., steam)for atomization. Furthermore, in embodiments in which the means forloading the reducing agent 150 comprises two or more injectors, in anembodiment, each of the injectors may be the same, or the means forloading the reducing agent 150 may comprise two or more differentinjectors (e.g., injector types, spray patterns, jet heads, atomizationmeans, etc.).

As will be appreciated, the specific location, configuration, andproperties of the means for loading the reducing agent 150 used in aNO_(x) removal system 100/100 a/100 b will vary depending on theparticular boiler configuration 101/101 a. For example, the reducingagent loading rate, location, structure and properties of the one ormore means for loading the reducing agent 150, strength of spray,droplet size, and amount of carrier fluid, among others, are eachspecifically designed to achieve a desired efficiency and/or NO_(x)level. Generally, however, by positioning the means for loading thereducing agent 150 downstream of the direct fire 103, and particularlyat or around a convection section for the exhaust gas stream 104, orjust downstream of the convection section, and/or at the flue gas outlet110, and preferably at both the convection section and the flue gasoutlet 110, a reduction in NO_(x) can be achieved with little if anyadverse effect on combustion in the burner or the heat transfer in theheat transfer tubes (whether fire or watertubes). Further, bypositioning the means for loading the reducing agent 150 downstream ofthe direct fire 103, and particularly at or around a turn-aroundlocation for the exhaust gas stream 104 and/or at the flue gas outlet110, preferably at both the convection section and the flue gas outlet110, minimal modifications are required to the boiler configuration101/101 a and the system 100/100 a/100 b can be readily fitted toexisting boilers or other fired vessels.

In an embodiment, the reducing agent 130 may be any reducing agent knownin the art, including, for example, aqueous ammonia, aqueous urea, orurea; however, in a preferred embodiment, the reducing agent is aqueousurea or aqueous ammonia.

In the embodiment shown, the reducing agent 130 is stored in a tank 131which is fed to the loading means 150 via line 132.

In an embodiment, the reducing agent 130 may be mixed with a carrierfluid, such as water, after storage in the tank 131 but prior to beingloaded into the boiler configuration 101/101 a. In a preferredembodiment, the carrier fluid (e.g., water) is mixed with the reducingagent on demand (i.e., the reducing agent and carrier fluid are notpre-mixed or stored as a carrier fluid/reducing agent mixture).

In particular, and with reference to the Figures, a carrier fluid supply120 (e.g., water supply) connects directly to the means for loading thereducing agent 150 via line 121

Mixing the reducing agent 130 with a carrier fluid dilutes the reducingagent. The reducing agent 130 decomposes prior to reacting in the boilerconfiguration 101/101 a; but typically, it is desirable to have thereducing agent 130 decompose at a strategic location in the boilerconfiguration 101/101 a which may not necessarily be the immediateloading site. The carrier fluid protects the reducing agent 130 until itcan reach a desired location, typically of a slightly lower temperatureat which the necessary reaction with NO_(x) and/or the SCR catalyst canoccur.

The exact dilution amount varies based on the specifics of the means forloading the reducing agent (e.g., location, type, etc.) and otherfactors relating to the boiler configuration 101/101 a, including, forexample, size of the boiler, volume of range of reducing agent that maybe injected, type of boiler, etc. The dilution amount is particularlyimportant when the reducing agent 130 loaded depends on the temperaturein the loading location and/or amount of NO_(x) formation. For example,when the reducing agent is provided downstream of the furnace and at oraround a convection section, typically a maximum 10% dilution (90%carrier fluid, 10% reducing agent) is used due to the highertemperatures experienced relative to other downstream locations. Incontrast, a maximum 20% dilution (80% carrier fluid, 20% reducing agent)is used when the reducing agent is provided downstream of the convectionsection and/or at or around the flue gas outlet 110.

Mixing the reducing agent 130 with a carrier fluid not only dilutes thereducing agent, but also influences the spray pattern of injection(e.g., promotes atomization). For example, as discussed further below,the amount of reducing agent 130 provided at any given point (via agiven means for providing the reducing agent 150) may vary. The carrierfluid can be used to make up volume if the amount of reducing agent 130injected is less than the maximum, resulting in maintaining a consistentspray pattern even when the amount of actual reducing agent isdecreased.

In accordance with some embodiments of the present disclosure, carrierfluid (e.g., water) alone is provided to the boiler/fired vessel via themeans for loading the reducing agent 150 in order to keep the loadingmeans clean and/or cool.

The flow rate/loading rate of the reducing agent also varies based onthe boiler/fired vessel parameters and the location of the specificmeans for loading the reducing agent 150. For example, generally theflow rate of the reducing agent when provided downstream of the directfire 103 and at or around a convection section is from 2 to 5 timesgreater than the maximum calculated flow rate based on an assumption of100% efficiency to account for loss of reducing agent due to thedegradation of the reducing agent at high temperatures. The flow rate ofthe reducing agent when provided downstream of the convection sectionand/or at or around the flue gas outlet 110 is less that that requiredat or around the convection section due to lower temperatures; however,the flow rate of the reducing agent downstream of the convection sectionand/or at or around the flue gas outlet 110 is still greater than thecalculated maximum based on an assumption of 100% efficiency.

In some embodiments, and as shown in FIGS. 1A-6, a metering pump 133controls the amount, flow rate and timing of reducing agent 130 providedto the means for loading the reducing agent 150. Depending on the designof the means for loading the reducing agent 150 (e.g., in embodiments inwhich the means for loading the reducing agent 150 is one or moreinjectors), a metering pump 133 may also control the means for loadingthe reducing agent 150.

In an embodiment, a control panel 170 may be used to program orotherwise control the metering pump 133. For example, in someembodiments, the control panel 170 may be in communication with at leastone sensor configured to detect one or more properties of theboiler/fired vessel and activate/deactivate the metering pump 133 inresponse to the detected property(ies). For example, the control panel170 may be in communication with one or more sensors configured todetect temperature at one or more locations, NO_(x) concentration at oneor more locations, firing rate, and combinations of these and otherproperties. In some embodiments, particularly one more than one loadingmeans 150 is provided, more than one sensor may be provided, with eachsensor in communication with a control panel 170. In some embodiments,each sensor is in communication with the same (e.g., master) controlpanel 170, while in other embodiments, designated control panels may beprovide for each sensor and, ultimately, loading means. The controlpanel 170 may then be configured to control the loading of the reducingagent based on input from the sensor(s).

For example, and as shown in the embodiments in the Figures, the controlpanel 170 is in communication with at least one temperature sensor 160,with the temperature sensor 160 located approximately adjacent the meansfor loading the reducing agent 150. In embodiments in which two or moreloading means 150 are provided, as shown in FIGS. 3A and 6, atemperature sensor 160 may be provided approximately adjacent eachloading means 150. In response to input from the temperature sensor 160,the control panel 170 causes the means for loading the reducing agent130 to load an amount of reducing agent 130 into the system 100/100a/100 b.

It will therefore be appreciated that the location of the temperaturesensor(s) 160 may therefore change based on the location of the meansfor loading the reducing agent 150. For example, as shown in FIGS. 1A,1B, and 4, the reducing agent 130 is loaded into the rear of the boilerconfiguration 101/101 a. The temperature sensor 160 is therefore locatedat the rear or bottom of the boiler configuration 101/101 a in proximityto the means for loading the reducing agent 150. As shown in FIGS. 2Aand 5, however, the temperature sensor 160 is located in the flue gasoutlet 110 because the reducing agent 130 is loaded into the flue gasoutlet 110. Further, as shown in FIGS. 3 and 6, multiple temperaturesensors 160 may be provided so that each means for loading the reducingagent 150 includes a corresponding temperature sensor 160 for itsspecific loading location. Other locations of the temperature sensor 160are contemplated based on the location of the means for loading thereducing agent 150.

In particularly, and with reference to the embodiments shown in whichthe reducing agent, preferably urea, is loaded at two locations, e.g.,as shown in FIGS. 3A and 6, the temperature sensor(s) 160 are incommunication with the control panel 170, which controls the activationof each of the injectors at the means for loading the reducing agent150. Further, and with particular reference to the embodiments shown inFIGS. 3A and 6, the control panel 170 is in communication with urea shutoff values 134, 135 on the urea lines 132 to a means for loading thereducing agent 150 either at the flue gas outlet 110 or downstream ofthe main flame 103 but before the flue gas outlet 110. In an embodiment,the urea shut off values may be solenoids.

The control panel 170 is configured to cause reducing agent 130 to beprovided to the system 100/100 a/100 b at temperatures greater than orequal to 425° F., as measured by the temperature sensors 160 locatednear the respective means for loading the reducing agent 150. Moreparticularly, in the embodiments shown in FIGS. 3A and 6, the controlpanel 170 is configured to cause reducing agent 130 to be preferablyprovided to the system 100 b at the flue gas outlet 110 when thetemperature read by the temperature sensor 160 at the flue gas outlet110 is greater than 425° F. In an embodiment, when the temperature readby the temperature sensor 160 at the flue gas outlet 110 is greater than425° F., the control panel 170 will cause reducing agent 130 to beprovided to the system 100 b primarily at the flue gas outlet 110 (e.g.,a majority of the reducing agent 130 provided to the system 100 b isprovided at the flue gas outlet 110). In other embodiments, when thetemperature read by the temperature sensor 160 at the flue gas outlet110 is greater than 425° F., the reducing agent 130 may be provided tothe system 100 b solely at the flue gas outlet 110.

As the temperature read by the temperature sensor 160 at the flue gasoutlet 110 reaches 425° F. or less, the control control scheme switchesfrom loading the reducing agent at the flue gas outlet 110 to loadingthe reducing agent at the convection section. In an embodiment, when thetemperature read by the temperature sensor 160 at the flue gas outlet110 is less than 425° F., the control panel 170 causes the reducingagent 130 to be provided primarily at the convection section of theboiler or other fired vessel (e.g., a majority of the reducing agent 130is provided to the system 100 b at the convection section). In otherembodiments, when the temperature read by the temperature sensor 160 atthe flue gas outlet 110 is less than 425° F., the reducing agent 130 maybe provided to the system 100 b solely at the convection section.

A temperature drop, such as to a temperature of less than 425° F.,usually occurs as the boiler's firing rate decreases or the demanddecreases. As the temperature drops significantly below 425° F., thereis a concern that the reducing agent (e.g., urea) will not completelydecompose if loaded to the flue gas outlet 110 as it passes through theSCR catalyst.

On the other end of the spectrum, typically the maximum temperature atwhich a reducing agent is loaded into the system 100/100 a/100 b is2,200° F. In an embodiment, the control panel 170 is configure to stopthe loading of the reducing agent to the system 100/100 a/100 b if thetemperature obtained by the sensor 160 is greater than 2,200° F. Attemperatures greater than 2,200° F., there is concern that the reducingagent, e.g., urea, may react with O₂ and form additional NO_(x).

In other embodiments, the control panel may cause all reducing agent 130to be provided at one strategic location (e.g., the furthest downstreamlocation or location closest to the SCR catalyst), provided thetemperature at that location remains within an operable range (e.g.,less than 2,200° F. and greater than 425° F.).

Preferably, the working loading temperature range for a given boilerconfiguration 101/101 a is from 1,000° F. to 2,200° F. It will beunderstood, however, that the workable and/or operable temperature rangefor a given system 100/100 a/100 b may vary depending on the specificreducing agent used.

In other embodiments, other sensors are used to monitor the overallfunction of the boiler/fired vessel 101/101 a. The control panel 170receives feedback from the sensors and determines whether adjustment tothe loading of the reducing agent is necessary. For example, a NO_(x)sensor may be provided at the flue gas outlet 110 for the purpose ofdetermining the overall NO_(x) concentration being released from thesystem 100/100 a/100 b. If the total NO_(x) is above a desired amount(e.g., a compliance or other regulatory amount), the control panel mayadjust the timing urea flow rate, concentration, dilution or one or moreof these and other factors of the system 100/100 a/100 b to bring theamount of NO_(x) into acceptable limits.

In some embodiments, the means for loading the reducing agent 150 isalso connected to an air supply 140 via lines 141. As shown in FIGS. 1A,3A and 4, in some embodiments, the air supply 140 connects both directlyto the means for loading the reducing agent 150, e.g., via line 142, toatomize the reducing agent/water mixture and to a covering around themeans for loading the reducing agent 150, e.g., via line 143, to coolthe means for loading the reducing agent 150 as needed. However, asshown in FIGS. 2A, 5 and 6, in some embodiments, the loading means 150may not include a covering around the means for loading the reducingagent 150 or may otherwise not require cooling. In such instances, theair supply 140 is connected to the means for loading the reducing agent150 via line 142 to atomize the reducing agent water mixture. In oneembodiment, the air supplied directly to the means for loading thereducing agent 150 for atomization via line 142 is a constant stream. Infurther embodiments, however, the air supplied directly to the means forloading the reducing agent 150 for atomization may vary based on thetotal loading volume, conditions in the boiler configuration 101/101a/101 b or NO_(x) removal system 100/100 a/100 b, and/or the particularboiler configuration 101/101 a or system 100/100 a/100 b. In any event,the amount of air provided by line 142 must be sufficient for properreducing agent atomization.

In some embodiments, the air supplied for cooling the loading means 150via line 143 is a constant stream. In other embodiments, however, theair supplied to the means for loading the reducing agent 150 via line143 may vary based on the temperature of the boiler configuration101/101 a, the temperature at the exit of the nozzles of the means forloading the reducing agent 150, the conditions necessary to achieveproper atomization of the reducing agent, and/or the temperaturenecessary to prevent destruction of the reducing agent.

In an embodiment, the SCR catalyst 111 may be any SCR catalyst known inthe art, including, for example, and without limitation, those made froma ceramic carrier (e.g., titanium oxide) with an oxide of a base metal(e.g., vanadium, molybdenum, tungsten, etc.), zeolite, or preciousmetal. In some embodiments, the catalytic components (e.g., carrier andthe oxide of base metal, zeolite or precious metal) may be packagedtogether on a structure such as a fiberglass structure. An exemplarypreferred catalyst is the DNX series (available from Haldor Topsoe)which is a corrugated monolith based on a glass fiber structure.

In an embodiment, the NO_(x) removal catalyst is then provided eithersimultaneously with the reducing agent at one location or downstreamfrom the reducing agent. Preferably, and in embodiments in which thereducing agent is provided at two or more locations, the NO_(x) removalcatalyst is provided downstream of the last of the two or more locationsat which the reducing agent is provided or simultaneously with thereducing agent at the last location that the reducing agent is provided.

Particularly, in the embodiments shown in FIGS. 1A, 2A, 3A and 4-6, theSCR catalyst 111 is provided at the flue gas outlet 110 such that thecombustion gases 104 pass through the structure on which the catalyst111 is contained. The SCR catalyst 111 accelerates the reductivereaction of the NO_(x) with the reducing agent 130. Therefore, thereducing agent 130 and the combustion gas 104 are mixed together at ornear the flue gas outlet 110 or in a passage of the exhaust gas 104 tothe flue gas outlet 110.

In a further embodiment, such as shown with reference to FIG. 2A, abaffle plate or mixing plate 109 may be used to promote mixing of thereducing agent 130 (or reducing agent/water mixture) with the NO_(x)removal catalyst 111. In the exemplary embodiment shown, the mixingplate 109 is provided in the passage of the flue gas outlet 110. While amixing plate 109 may be provided at the flue gas outlet 110 regardlessof the location of the means for loading the reducing agent 150, it willbe understood that the utility of the mixing plate 109 is most importantwhen the means for loading the reducing agent 150 is provided at theflue gas outlet 110.

As shown in FIGS. 2A and 5, in such an embodiment as when the means forloading the reducing agent 150 is provided at the flue gas outlet 110,the mixing plate 109 is provided at a location just above (e.g.,downstream) from the means for loading the reducing agent 150. Thispositioning ensures that the reducing agent 130 (or reducing agent/watermixture) is received in the flue gas outlet 110 before encountering themixing plate 109.

One skilled in the art will understand that the functionality of amixing plate 109 as described above can be maximized when the flue gasoutlet 110 is made of round outlet ducts. In embodiments in which theoutlet ducts are rectangular, enhanced mixing of the reducing agent (orreducing agent/water mixture) may be best provided by using multiplemeans for loading the reducing agent 150 or a means for loading thereducing agent 150 with multiple outlets/nozzles.

In accordance with one embodiment, a method of NO_(x) removal for usewith a boiler or other fired vessel is disclosed.

In an embodiment, the method includes providing a reducing agent to aboiler or other fired vessel downstream of the direct fire and providinga selective catalytic reduction catalyst downstream from the reducingagent. In an embodiment, the boiler or other fired vessel is any boileror other fired vessel as disclosed herein. In a further embodiment, theboiler or other fired vessel is selected from the group consisting of afiretube boiler and a watertube boiler.

In a further embodiment, the reducing agent is provided to the boiler orother fired vessel at or around the location at which the exhaust gasesturn to a convection area of the boiler or other fired vessel or in theexhaust gas stream. In a further embodiment in which the boiler or otherfired vessel is a firetube boiler, the reducing agent is provided to theboiler at the rear turn around space. In a further embodiment in whichthe boiler or other fired vessel is a watertube boiler, the reducingagent is provided at the point at which the exhaust gases turn to enterthe hot end of the convection zone. In a further embodiment, thereducing agent is provided to the boiler or other fired vessel at theflue gas outlet.

In one embodiment, the step of providing a reducing agent to a boiler orother fired vessel comprises injecting the reducing agent. In anotherembodiment, the boiler or other fired vessel is a boiler and thereducing agent is injected downstream of the direct fire. In a furtherembodiment, the boiler or other fired vessel is a firetube or watertubeboiler and the reducing agent is injected downstream of the direct fire.In a further embodiment, the boiler or other fired vessel is a firetubeboiler and the reducing agent is injected at the rear turn around spaceor the flue gas outlet. In a further embodiment, the boiler or otherfired vessel is a watertube boiler and the reducing agent is injected atthe point at which the exhaust gases turn to enter the hot end of theconvection zone or the flue gas outlet.

In a further embodiment, the step of providing a reducing agent to aboiler or other fired vessel includes injecting and atomizing thereducing agent.

In an embodiment, the step of providing a reducing agent to a boiler orother fired vessel comprises controlling the amount of reducing agentprovided and when the reducing agent is provided. In one embodiment, thestep of controlling the amount of reducing agent provided and when thereducing agent is provided includes monitoring the temperature of theboiler at the point at which the reducing agent is provided andproviding the reducing agent only when the temperature is within anoperable range as determined by the particular reducing agent and/or SCRcatalyst used. In an embodiment, the reducing agent is urea and thetemperature is within a range sufficient to convert the urea to ammonia.

In an embodiment, the method further includes mixing the reducing agentwith water prior to providing the reducing agent to a boiler or otherfired vessel. In an embodiment, the mixing the reducing agent with wateroccurs in the providing means.

In an embodiment, the method further includes mixing the reducing agentwith the exhaust gas stream. In an embodiment, the method includesproviding or injecting the reducing agent at the flue gas outlet of theboiler or other fired vessel and mixing the reducing agent with the fluegas.

In one embodiment, the reducing agent is aqueous urea.

In an embodiment, the step of providing a selective catalytic reductioncatalyst downstream from the reducing agent comprises providing theselective catalytic reduction catalyst at the flue gas outlet.

In accordance with one embodiment, a method of retrofitting a boiler orother fired vessel with a NO_(x) removal system is disclosed. In anembodiment, the boiler or other fired vessel comprises a housing with afurnace and burner at one end, a convection section at the other end ofthe housing, and a flue gas outlet at the end of the convection section.In a further embodiment, the boiler or other fired vessel is selectedfrom the group consisting of a gas and/or oil fired burner, a steamboiler with or without superheat, a hot water boiler, and a thermalfluid heater of the firetube or watertube variety. Preferably, theboiler or other fired vessel is a firetube boiler or a watertube boiler.

The method next includes determining one or more parameters of theexisting boiler or other fired vessel, and preferably determining atleast two, or at least three, or at least four parameters of theexisting boiler or other fired vessel. Exemplary parameters include, butare not limited to, internal shape of the furnace, internal shape of theconvection section, internal shape of the flue gas outlet, peaktemperature at the furnace, peak temperature at the convection section,peak temperature at the flue gas outlet, operable temperature range atthe furnace, operable temperature range at the convection section,operable temperature range at the flue gas outlet, concentration rangeof NO_(x) formation, operable firing range, type of NO_(x) compoundsformed and amounts of each kind/class, operating conditions causing peakNO_(x) formation, expected NO_(x) reductions, emissions requirements andcombinations of these and other parameters.

In an embodiment, the step of determining one or more parameters of theexisting boiler or other fired vessel includes determining at least oneof the peak temperatures at the convection section and operabletemperature range at the flue gas outlet. In an embodiment, the step ofdetermining one or more parameters of the existing boiler or other firedvessel includes determining preferably at least both the peaktemperature at the convection section and operable temperature range atthe flue gas outlet. The parameter of the peak temperature of theconvection section will help determine whether a reducing agent may beloaded to the convection section and, if so, at what conditions. Theparameter of the operable temperature range of the flue gas outlet willhelp determine whether a reducing agent may be loaded to the flue gasoutlet and, if so, at what conditions.

The method next includes determining, based on the one or moreparameters of the existing boiler or other fired vessel, at least one,preferably two or more, more preferably three or more, and morepreferably four or more parameters for a NO_(x) removal system. Suchparameters include, for example, but are not limited to, reducingagent(s) to be used, SCR catalyst(s) to be used, reducing agent loadingpoint(s) (including how the mixing length of the flue gas outlet betweenany potential reducing agent loading sites and the location of the SCRcatalyst(s)), reducing agent loading time(s) (e.g., based on one or moretemperatures, NO_(x) formation, operating conditions of the boiler/firedvessel, etc.), type of means for loading the reducing agent, spraypattern of the means for loading the reducing agent, dilution ordilution range for loading the reducing agent, and combinations of theseand other parameters.

In an embodiment, the step of determining, based on the one or moreparameters of the existing boiler or other fired vessel, at least oneparameter for a NO_(x) removal system includes determining at least oneof the dilution or dilution range of the reducing agent, the spraypattern of any one or more means for loading the reducing agent, and thereducing agent to be used at the flue gas outlet. Preferably the step ofdetermining, based on the one or more parameters of the existing boileror other fired vessel, at least one parameter for a NO_(x) removalsystem includes at least two, or more preferably all three ofdetermining at least one of the dilution or dilution range of thereducing agent, the spray pattern of any one or more means for loadingthe reducing agent, and the reducing agent to be used at the flue gasoutlet.

In embodiments in which more than one means for loading a reducing agentwill be used in a NO_(x) removal system, and particularly in embodimentsin which at least two of the more than one means for loading a reducingagent will be located at different positions of the boiler or otherfired vessel, the step of determining, based on the one or moreparameters of the existing boiler or other fired vessel, at least oneparameter for a NO_(x) removal system includes at least one ofdetermining the dilution or dilution range of the reducing agent to beloaded at a first location in the boiler or other fired vessel,determining the dilution or dilution range or the reducing agent to beloaded at a second location in the boiler or other fired vessel,determining the spray pattern of at least one of the more than one meansfor loading the reducing agent, and the reducing agent to be used withat least one of the more than one means for loading the reducing agent.

In an embodiment, the method further includes providing at least oneproviding means in communication with the housing for providing areducing agent in the housing of the boiler or other fired vessel inaccordance with the one or more parameters of the existing boiler orother fired vessel determined in the previous step.

In a particular embodiment, the method includes providing a first atleast one means in communication with the housing for providing areducing agent in the housing of the boiler or other fired vesseldownstream of the furnace and upstream of the flue gas outlet andproviding a second at least one means in communication with the housingfor providing a reducing agent in the housing of the boiler or otherfired vessel downstream of the first at least one means for providing areducing agent. Preferably, the first means in communication with thehousing for providing a reducing agent comprises at least two injectorsand is located at the convection section of the boiler and the secondmeans in communication with the housing for providing a reducing agentis located at the flue gas outlet.

In an embodiment, the method further includes introducing a selectivecatalytic reduction (SCR) catalyst at the flue gas outlet of the boileror other fired vessel in accordance with the one or more parameters ofthe existing boiler or other fired vessel determined in a previous step.

In still further embodiments, the method further includes providing atleast one additional component as necessary to control the providing ofa reducing agent and/or SCR catalyst based on the parameters for theNO_(x) removal system determined earlier, wherein the at least oneadditional component is selected from the group consisting of atemperature sensor in communication with the housing, a metering pump incommunication with the at least one providing means, a control panel incommunicating with the at least one providing means and/or the meteringpump, a water source connected to the at least one providing means, andan air source connected to the at least one providing means.

The following embodiments are provided as specific support and/orenablement for the appended claims. According, the present disclosureprovides:

E1. A boiler or other fired vessel assembly comprising a housingcomprising a burner at a first end, a furnace downstream of the burner,a convection section downstream of the furnace, and a flue gas outletdownstream of the convection section; a first means for loading areducing agent into the housing, wherein the first means for loading thereducing agent is located downstream of the furnace and comprises atleast two injectors; a second means for loading a reducing agent intothe housing, wherein the second means for loading the reducing agent islocated downstream of the first means for loading the reducing agent andcomprises at least one injector; and a selective catalytic reduction(SCR) catalyst located either downstream of the second means for loadinga reducing agent into the housing or adjacent the second means forloading a reducing agent into the housing such that the SCR catalyst isprovided to the boiler or other fired vessel approximatelysimultaneously with the reducing agent from the second means for loadingthe reducing agent into the housing.

E2. The assembly of E1, wherein the second means for loading thereducing agent comprises at least two injectors.

E3. The assembly of any of E1-E2, wherein the first means for loading areducing agent is located at the convection section.

E4. The assembly of any of E1-E3, wherein the second means for loading areducing agent is located at the flue gas outlet.

E5. The assembly of any of E1-E4, wherein the SCR catalyst is located atthe flue gas outlet.

E6. The assembly of any of E1-E5, further including a mixing element atthe flue gas outlet downstream of the second means for loading areducing agent.

E7. The assembly of any of E1-E6, further comprising a metering pump incommunication with at least one of the first or second means for loadinga reducing agent.

E8. The assembly of any of E1-E7, further comprising a temperaturesensor proximal to at least one of the first or second means for loadinga reducing agent.

E9. The assembly of any of E1-E8, further including a storage tankcomprising the reducing agent and connected to at least one of the firstor second means for loading a reducing agent.

E10. The assembly of any of E1-E9, further including a water supplyconnected to at least one of the first or second means for loading areducing agent.

E11. The assembly of any of E1-E10, further including an air supplyconnected to at least one of the first or second means for loading areducing agent.

E12. The assembly of any of E1-E11, wherein the reducing agent isaqueous ammonia or aqueous urea.

E13. The assembly of any of E1-E12, wherein the boiler or other firedvessel is a boiler.

E14. The assembly of E13, wherein the boiler is a firetube boiler or awatertube boiler.

E15. A boiler or other fired vessel assembly comprising a housingcomprising a burner, an intermediate furnace, a convection sectiondownstream from the intermediate furnace, and a flue gas outletdownstream of the convection section; a first means for loading areducing agent into the housing, wherein the first means for loading thereducing agent is located downstream of the furnace and comprises atleast two injectors; a second means for loading a reducing agent intothe housing, wherein the second means for loading the reducing agent islocated downstream of the first means for loading the reducing agent andcomprises at least one injector; and a selective catalytic reduction(SCR) catalyst located either downstream of the second means for loadinga reducing agent into the housing or adjacent the second means forloading a reducing agent into the housing such that the SCR catalyst isprovided to the boiler approximately simultaneously with the reducingagent from the second means for loading the reducing agent into thehousing.

E16. The assembly of E15, wherein the boiler or other fired vessel is aboiler.

E17. The assembly of E16, wherein the boiler is a firetube boiler or awatertube boiler.

E18. A method of reducing NO_(x) in a boiler or other fired vessel whichproduces a direct flame, the method comprising: providing (a) a firstamount of a reducing agent to the boiler or other fired vessel at afirst location downstream of the direct flame when a temperature of thefirst location is greater than or equal to a threshold temperature, or(b) a second amount of reducing agent to the boiler or other firedvessel at a second location downstream of the direct flame when atemperature of the first location is less than the thresholdtemperature, wherein the first location is downstream of the secondlocation; and providing a selective catalytic reduction catalyst eitherdownstream of or at generally the same location as second amount of areducing agent, wherein the second amount of reducing agent is providedusing at least two injectors.

E19. The method of E18, wherein the boiler or other fired vesselcomprises a housing with a burner and furnace at one end, a convectionsection at a second end, and the flue gas outlet at the end of theconvection section and wherein the step of providing a second amount ofa reducing agent includes providing the reducing agent to the convectionsection, the step of providing a first amount of reducing agent includesproviding the reducing agent to the flue gas outlet, and the step ofproviding a selective catalytic reduction catalyst includes providingthe selective catalytic reduction catalyst to the flue gas outlet.

E20. The method of any of E18-E19, wherein the threshold temperature is425° F.

E21. The method of claim any of E18-E20, further comprising the step ofmixing the reducing agent with a carrier fluid before providing thefirst amount or second amount of the reducing agent.

E22. The method of any of E18-E21, wherein the boiler or other firedvessel is a boiler.

E23. The method of E22, wherein the boiler is a firetube boiler or awatertube boiler.

E24. A method of retrofitting a boiler or other fired vessel, the boileror other fired vessel comprising a housing with a burner, anintermediate furnace, a convection section downstream of the furnace,and a flue gas outlet downstream of the convection section, with aNO_(x) removal system, the method comprising: determining one or moreparameters of the boiler or other fired vessel, wherein at least one ofthe one or more parameters is selected from the group consisting ofinternal shape of the boiler or other fired vessel, internal shape ofthe furnace, internal shape of the convection section, internal shape ofthe flue gas outlet, peak temperature of the furnace, peak temperatureof the convection section, peak temperature of the flue gas outlet,operable temperature range of the furnace, operable temperature range ofthe convection section, operable temperature range of the flue gasoutlet, concentration range of NO_(x) formation, operable firing range,type of NO_(x) compounds and concentration range of one or more types ofNO_(x) compounds, operating conditions causing peak NO_(x) formation andcombinations thereof; determining one or more parameters of a NO_(x)removal system, wherein at least one of the one or more parameters isselected from the group consisting of SCR catalyst to be used, reducingagent to be used, number of reducing agent loading points, locations ofreducing agent loading points, type of means for loading reducing agent,timing of reducing agent loading at each reducing agent loading point,concentration of reducing agent loading at each reducing agent loadingpoint, spray pattern of the means for loading reducing agent at eachreducing agent loading point, dilution or dilution range of the reducingagent, and combinations thereof; providing, based on the one or moreparameters of the NO_(x) removal system, a first means in communicationwith the housing for providing a reducing agent into the housing of theboiler or other fired vessel downstream of the furnace, wherein thefirst means comprises at least two injectors; providing, based on theone or more parameters of the NO_(x) removal system, a second means incommunication with the housing for providing a reducing agent into thehousing of the boiler or other fired vessel downstream of the firstmeans for providing reducing agent; and providing, based on the one ormore parameters of the NO_(x) removal system, a selective catalyticreduction catalyst downstream from or simultaneously with the secondmeans for providing a reducing agent.

E25. The method of E24, further comprising providing at least oneadditional component selected from the group consisting of a temperaturesensor in communication with the housing, a metering pump incommunication with at least one of the first and second means forproviding a reducing agent, a control panel in communication with the atleast one of the first and second means for providing a reducing agentand/or the metering pump, a water source connected to at least one ofthe first and second means for providing a reducing agent, and an airsource connected to at least one of the first and second means forproviding a reducing agent.

E26. The method of any of E24-E25, wherein the step of determining oneor more parameters of the boiler or other fired vessel comprisesdetermining at least one of the peak temperature at the convectionsection and the operable temperature range at the flue gas outlet.

E27. The method of any of E24-E26, wherein the step of determining oneor more parameters of a NO_(x) removal system comprises determining atleast one of the dilution of the reducing agent to be loaded to theconvection section of the boiler or other fired vessel, the spraypattern of at least one means for providing a reducing agent, and thereducing agent to be used.

E28. The method of any of E24-E27, wherein the boiler or other firedvessel is selected from the group consisting of a firetube boiler and awatertube boiler.

E29. A boiler assembly comprising: a housing comprising a burner at afirst end, a furnace downstream of the burner, a convection sectiondownstream of the furnace, and a flue gas outlet downstream of theconvection section; a first means for loading a reducing agent into thehousing, wherein the first means for loading the reducing agent islocated downstream of the furnace and comprises at least two injectors;a second means for loading a reducing agent into the housing, whereinthe second means for loading the reducing agent is located downstream ofthe first means for loading the reducing agent and comprises at leastone injector; and a selective catalytic reduction (SCR) catalyst locatedeither downstream of the second means for loading a reducing agent intothe housing or adjacent the second means for loading a reducing agentinto the housing such that the SCR catalyst is provided to the boilerapproximately simultaneously with the reducing agent from the secondmeans for loading the reducing agent into the housing.

E30. The assembly of E29, wherein the second means for loading thereducing agent comprises at least two injectors.

E31. The assembly of any of E29-E30, wherein the first means for loadinga reducing agent is located at the convection section.

E32. The assembly of any of E29-E31, wherein the second means forloading a reducing agent is located at the flue gas outlet.

E33. The assembly of any of E29-E32, wherein the SCR catalyst is locatedat the flue gas outlet.

E34. The assembly of any of E29-E33, further including a mixing elementat the flue gas outlet downstream of the second means for loading areducing agent.

E35. The assembly of any of E29-E34, further comprising a metering pumpin communication with at least one of the first or second means forloading a reducing agent.

E36. The assembly of any of E29-E35, further comprising a temperaturesensor proximal to at least one of the first or second means for loadinga reducing agent.

E37. The assembly of any of E29-E36, further including a storage tankcomprising the reducing agent and connected to at least one of the firstor second means for loading a reducing agent.

E38. The assembly of any of E29-E37, further including a water supplyconnected to at least one of the first or second means for loading areducing agent.

E39. The assembly of any of E29-E38, further including an air supplyconnected to at least one of the first or second means for loading areducing agent.

E40. The assembly of any of E29-E39, wherein the reducing agent isaqueous ammonia or aqueous urea.

E41. The assembly of any of E29-E40, wherein the boiler is a firetubeboiler or a watertube boiler.

E42. A boiler assembly comprising a housing comprising a burner, anintermediate furnace, a convection section downstream from theintermediate furnace, and a flue gas outlet downstream of the convectionsection; a first means for loading a reducing agent into the housing,wherein the first means for loading the reducing agent is locateddownstream of the furnace and comprises at least two injectors; a secondmeans for loading a reducing agent into the housing, wherein the secondmeans for loading the reducing agent is located downstream of the firstmeans for loading the reducing agent and comprises at least oneinjector; and a selective catalytic reduction (SCR) catalyst locatedeither downstream of the second means for loading a reducing agent intothe housing or adjacent the second means for loading a reducing agentinto the housing such that the SCR catalyst is provided to the boilerapproximately simultaneously with the reducing agent from the secondmeans for loading the reducing agent into the housing.

E43. The assembly of E42, wherein the boiler is a watertube boiler or afiretube boiler.

E44. A method of reducing NO_(x) in a boiler which produces a directflame, the method comprising: providing (a) a first amount of a reducingagent to the boiler at a first location downstream of the direct flamewhen a temperature of the first location is greater than or equal to athreshold temperature, or (b) a second amount of reducing agent to theboiler at a second location downstream of the direct flame when atemperature of the first location is less than the thresholdtemperature, wherein the first location is downstream of the secondlocation; and providing a selective catalytic reduction catalyst eitherdownstream of or at generally the same location as second amount of areducing agent, wherein the first amount of reducing agent is providedusing at least two injectors.

E45. The method of E44, wherein the boiler comprises a housing with aburner and furnace at one end, a convection section at a second end, andthe flue gas outlet at the end of the convection section and wherein:the step of providing a second amount of a reducing agent includesproviding the reducing agent to the convection section, the step ofproviding a first amount of reducing agent includes providing thereducing agent to the flue gas outlet, and the step of providing aselective catalytic reduction catalyst includes providing the selectivecatalytic reduction catalyst to the flue gas outlet.

E46. The method of any of E44-E45, wherein the threshold temperature is425° F.

E47. The method of claim any of E44-E46, further comprising the step ofmixing the reducing agent with a carrier fluid before providing thefirst amount and second amount of the reducing agent.

E48. The method of any of E44-E47, wherein the boiler is a firetubeboiler or a watertube boiler.

E49. A method of retrofitting a boiler, the boiler comprising a housingwith a burner, an intermediate furnace, a convection section downstreamof the furnace, and a flue gas outlet downstream of the convectionsection, with a NO_(x) removal system, the method comprising:determining one or more parameters of the boiler, wherein at least oneof the one or more parameters is selected from the group consisting ofinternal shape of the boiler or other fired vessel, internal shape ofthe furnace, internal shape of the convection section, internal shape ofthe flue gas outlet, peak temperature of the furnace, peak temperatureof the convection section, peak temperature of the flue gas outlet,operable temperature range of the furnace, operable temperature range ofthe convection section, operable temperature range of the flue gasoutlet, concentration range of NO_(x) formation, operable firing range,type of NO_(x) compounds and concentration range of one or more types ofNO_(x) compounds, operating conditions causing peak NO_(x) formation andcombinations thereof; determining one or more parameters of a NO_(x)removal system, wherein at least one of the one or more parameters isselected from the group consisting of SCR catalyst to be used, reducingagent to be used, number of reducing agent loading points, locations ofreducing agent loading points, type of means for loading reducing agent,timing of reducing agent loading at each reducing agent loading point,concentration of reducing agent loading at each reducing agent loadingpoint, spray pattern of the means for loading reducing agent at eachreducing agent loading point, dilution or dilution range of the reducingagent, and combinations thereof; providing, based on the one or moreparameters of the NO_(x) removal system, a first means in communicationwith the housing for providing a reducing agent into the housing of theboiler downstream of the furnace, wherein the first means comprises atleast two injectors; providing, based on the one or more parameters ofthe NO_(x) removal system, a second means in communication with thehousing for providing a reducing agent into the housing of the boilerdownstream of the first means for providing reducing agent; andproviding, based on the one or more parameters of the NO_(x) removalsystem, a selective catalytic reduction catalyst downstream from orsimultaneously with the second means for providing a reducing agent.

E50. The method of E49, further comprising providing at least oneadditional component selected from the group consisting of a temperaturesensor in communication with the housing, a metering pump incommunication with at least one of the first and second means forproviding a reducing agent, a control panel in communication with the atleast one of the first and second means for providing a reducing agentand/or the metering pump, a water source connected to at least one ofthe first and second means for providing a reducing agent, and an airsource connected to at least one of the first and second means forproviding a reducing agent.

E51. The method of any of E49-E50, wherein the step of determining oneor more parameters of the boiler or other fired vessel comprisesdetermining at least one of the peak temperature at the convectionsection and the operable temperature range at the flue gas outlet.

E52. The method of any of E49-E51, wherein the step of determining oneor more parameters of a NO_(x) removal system comprises determining atleast one of the dilution of the reducing agent to be loaded to theconvection section of the boiler or other fired vessel, the spraypattern of at least one means for providing a reducing agent, and thereducing agent to be used.

E53. The method of any of E49-E52, wherein the boiler is selected fromthe group consisting of a firetube boiler and a watertube boiler.

The numerical ranges disclosed herein include all values from, andincluding, the lower value and the upper value. For ranges containingexplicit values (e.g., 1 or 2, or 3 to 5, or 6, or 7) any subrangebetween any two explicit values is included (e.g., 1 to 2; 2 to 6; 5 to7; 3 to 7; 5 to 6; etc.).

Among other things, it should be appreciated that the scope of thepresent disclosure is not limited to the number of constitutingcomponents, the materials thereof, the shapes thereof, the relativearrangement thereof, etc., as described above, but rather the abovedisclosures are simply provided as example embodiments.

Thus, it is specifically intended that the present invention not belimited to the embodiments and illustrations contained herein, butinclude modified forms of those embodiments including portions of theembodiments and combinations of elements of different embodiments ascome within the scope of the following claims.

What is claimed is:
 1. A boiler or other fired vessel assemblycomprising: a housing comprising a burner at a first end, a furnacedownstream of the burner, a convection section downstream of thefurnace, and a flue gas outlet downstream of the convection section; afirst means for loading a reducing agent into the housing, wherein thefirst means for loading the reducing agent is located downstream of thefurnace and comprises at least two injectors; a second means for loadinga reducing agent into the housing, wherein the second means for loadingthe reducing agent is located downstream of the first means for loadingthe reducing agent and comprises at least one injector; a selectivecatalytic reduction (SCR) catalyst located either downstream of thesecond means for loading a reducing agent into the housing or adjacentthe second means for loading a reducing agent into the housing such thatthe SCR catalyst is provided to the boiler or other fired vesselapproximately simultaneously with the reducing agent from the secondmeans for loading the reducing agent into the housing; a temperaturesensor located at the second means for loading a reducing agent; acontrol panel in communication with the temperature sensor, the controlpanel being configured to control loading of the reducing agent into thehousing by the first means for loading a reducing agent and the secondmeans for loading a reducing agent, wherein the control panel is furtherconfigured to cause the reducing agent to be provided by the secondmeans for loading a reducing agent when a temperature measured by thetemperature sensor is greater than or equal to a threshold temperature.2. The assembly of claim 1, wherein the second means for loading thereducing agent comprises at least two injectors.
 3. The assembly ofclaim 1, wherein the first means for loading a reducing agent is locatedat the convection section.
 4. The assembly of claim 1, wherein thesecond means for loading a reducing agent is located at the flue gasoutlet.
 5. The assembly of claim 1, wherein the SCR catalyst is locatedat the flue gas outlet.
 6. The assembly of claim 1, further including amixing element at the flue gas outlet downstream of the second means forloading a reducing agent.
 7. The assembly of claim 1, further comprisinga metering pump that is controlled by the control panel, the meteringpump being in communication with at least one of the first or secondmeans for loading a reducing agent.
 8. The assembly of claim 1, whereinthe control panel is further configured to cause the reducing agent tobe provided by the first means for loading a reducing agent when atemperature measured by the temperature sensor is less than thethreshold temperature.
 9. The assembly of claim 1, further including awater supply connected to at least one of the first or second means forloading a reducing agent.
 10. The assembly of claim 1, further includingan air supply connected to at least one of the first or second means forloading a reducing agent.
 11. The assembly of claim 1, wherein theboiler or other fired vessel further comprises a rear turn around spacebetween the furnace and the convection section, and the first means forloading a reducing agent is located at the rear turn around space. 12.The assembly of claim 11, wherein the boiler or other fired vessel is afiretube boiler or a watertube boiler.